1. Field of the Invention
This invention relates to a supersonic transducer, and more particularly to a supersonic transducer which detects a frequency signal to be energized under varying temperature and load conditions which result in a varying resonant frequency.
2. Description of the Prior Art
In an electrostrictive vibrator, piezo-electric electrostrictive materials such as lead titanate zirconate are utilized. It is possible to produce various shaped vibrators because the powder of the above electrostrictive material is poured into a mold when produced. For example, the vibrator may have shapes such as cylindrical, circular disc, rectangular plate, prismatic, or other shapes may be produced depending upon its desired utility. Also, since a polarization is applied after it is unglazed, the orientation of the polarization may be freely selected. Since it is a strong dielectric, its electric capacity is large and, as its electric impedance is very small, the energizing voltage to be applied between both electrodes may be small, and accordingly it has characteristics very easily controlled. Thus, it may be utilized in many fields. There is known in the art one type of vibrator known as Langevin's vibrator for producing a resonant frequency of several kHz by placing an electrostrictive vibrator between two metal blocks. One problem associated with such electrostrictive vibrators is the variation of resonant frequeny of the vibrator according to the temperature and load conditions. The frequency of the energizing voltage may be displaced thereby, and it may become impossible to vibrate the device. When the Q factor generally becomes high so that the mechanical resonance of its vibrating system is operating at its peak, the foregoing tendency becomes serious. From such reasons, various structures have been tried for positively detecting the resonant frequency of the vibrator and for feeding back the detected signal to an oscillator for automatic tuning of the same. This type of vibrator typically provides a feedback electrode in addition to an energizing electrode for picking up a signal corresponding to the resonant frequency. In other words, a detecting pick-up element is provided in the vibrator, and generally it performs effectively, but since its detected voltage is extremely low, its electrical control is difficult. Also, if the area of the feedback electrode is enlarged, it tends to vibrate effectively so that it cannot obtain the desired results.
In addition to the above system, there exists in the prior art means for electrical detection by utilizing a bridge circuit, or a known method by mechanical means, but they require an artificial load, and are difficult to control electrically.